The present invention relates to the production of pattern equipment used in manufacturing, and in particular, to a method for defining complex geometries which are transposed into tooling used to produce automotive components.
Various automotive components, for example cylinder heads, include complex geometric shapes. The production of tooling which is used to cast complex geometric shapes has required a combination of engineering design, pattern making, and casting experimentation, to produce molds which produce acceptable components.
Typically, past methods for producing molds for complex geometries have begun in the laboratory, where clay models of the components are tested and refined. For example, a clay model of cylinder head design is engineered, and then tested and refined in the laboratory by adding and removing material to provide desired air flow characteristics. Thus, the air flow channels through such parts are not simple cylinders, but complex shapes. A "master flow box" is then made from the clay model by filling its flow channels with a compound, such as a liquid plastic or sand and adhesive mix, which hardens in the shape of the flow channels. Thereafter, the clay is removed, leaving a male mold which is placed in a perimeter mold to replicate the flow channels. A "master flow box" is then made of a permanent material, such as a plastic, poured into the perimeter mold. The master flow box is split open and the male molds removed. The master flow box is reassembled and the air flow therethrough is checked, and minor design changes made, as needed.
Drawings are then produced by direct, physical measurement of the master flow box. In turn, the completed drawings are measured at selected intervals to generate data for input into a computer-aided design (CAD) system. The CAD data is used to create additional drawings and to perform further engineering analysis of the characteristics of the particular component. However, the generation of CAD data from drawings produced by direct physical measurement of the master flow box involves a lengthy design process. This problem has been partially overcome with more recent CAD systems which are capable of receiving data input directly from a fine-tipped stylus which is traced over the flow channel contours of the master flow box at predetermined intervals. Drawings are then made from the CAD data with the CAD system, and the overall time required to obtain both drawings and CAD data is reduced. However, with both measurement procedures many nuances and subtleties in the surfaces of the master flow box are lost because the measurements are made at defined intervals between which small but significant variations in the flow channel surfaces have been defined.
After the CAD data is developed, a tape of the CAD data (hereafter, a CAD tape) is converted to a numerical control tape (hereafter, an NC tape) by a specialized, numerically controlled machine (hereafter, NC machine), for use on the NC machine. In the conversion process, the NC machine interpolates the CAD data to produce an NC tape with many times the data of the CAD tape. The data is also modified to expand the flow channel dimensions a small percentage to allow for shrinkage of the molded forms therein during production. Production partings for separation of the mold parts are also defined at this point. The NC machine then reads the NC tape which controls the motion of cutters to produce a "master model" of the mold shape out of metal. The operability of the production partings is then tested by casting male molds with the master model, and changes in the production partings made as needed. Once a suitable master model is obtained, numerous replicas thereof may be made with the NC tape to serve as production tooling.
In the conversion of CAD data to NC data, the interpolation process further smooths out the subtleties and nuances of complex geometric surfaces, causing a loss of these design features in the master model. Although more data could be taken when inputting the CAD data, sufficient data for an NC machine to produce a master model of a complex geometric surface would overwhelm the data handling capabilities of currently available CAD systems. The amount of data sufficient to produce a CAD drawing, and generate CAD surfaces for further engineering design purposes, may be as much as ten times less than that required for the NC tape.
Additional problems have been experienced in practice at this stage in the development of tooling. From a practical standpoint, the specialized NC machine required to provide data conversion from CAD data to NC data is expensive, and therefore is owned by a more limited number of vendors than otherwise are available for production of master models by numerically controlled machining.
Alternatively, a master model may be produced with some accuracy independently of the CAD data, by directly inputting data from the master flow box into an NC tape. NC machines are now also capable of receiving data input directly from a cutter-shaped stylus which is traced over the contours of the master flow box at predetermined intervals to define the cutter path. Using this capability, one option is to make a direct NC tape from the master flow box. Production partings are added, allowance for shrinkage made, and a fairly precise master model made from the NC tape. Another option produces equally precise master models without using either CAD data or making an NC tape, by using an NC duplicating machine. The cutter of an NC duplicating machine mimics the path of a cutter-shaped stylus which is simultaneously traced over the surface of a master flow box. The cutter thereby duplicates the shape directly in metal to produce a master model, without necessitating the creation of an NC tape. However, when these methods are used, a separate CAD data base is generated to produce drawings and conduct further engineering analysis. There is, thus, no formal interrelation between the CAD and NC data bases.
Regardless of the method used to develop CAD data or NC data, all of the methods share additional drawbacks. From a practical standpoint, even major manufacturers typically engage vendors (machine shops having NC machines) to produce the master models from vendor-made NC tapes or with NC duplicating machines. Because several vendors are typically used to produce tooling in production quantities, and each defines different production partings. Variations and inaccuracies in tooling appear from vendor to vendor. In turn, the resulting component variation can affect product performance. For example, where such tooling produces automobile engine parts, variability in the production engines results, effecting fuel economy and emissions performance.
Another, more significant problem is experienced by all methods which use a stylus to trace the surfaces of complex geometries, whether to input CAD data or NC data. Erroneous data is entered when the stylus is passed over a boundary between surfaces which forms a sharp angle, right angle, or other rapid transition between surfaces. For example, when a stylus traces from the surface of a flow channel in a master flow box over an edge to a plane at which the master flow box is separated, erroneous data is produced which defines irregularities at the edge not present in the master flow box. FIG. 2 shows a plot of CAD data so entered at an edge of a flow box, showing this "edge effect". Where this problem occurs in entering NC data with a stylus, an NC machine will cut irregularities into the workpiece which must be corrected by additional hand work.
In summary, the variations and inconsistencies from original component design are introduced into production in a number of ways. Prior art methods of surface measurement, data entry, and data translation result in errors and inconsistencies in the drawings, CAD data and NC data compared to the original design Moreover, these errors, inconsistencies and variations remain uncorrected, as no effective way exists to enter corrections back into the data bases. Similarly, no cost-effective way exists to modify the data bases to enter design improvements arising from further engineering, or from casting experimentation. Rather, the NC data and CAD data must be re-entered to produce drawings and NC tapes for production, allowing opportunities for further error.
Further, there is no reverse engineering capability or method which permits the surfaces of the master model, production tooling, used tooling, or castings produced therewith, to be compared against either the CAD data or NC data for precision during production, or monitoring during use. Direct physical measurement and physical comparison with the master flow box remains necessary. As a result, quality control of tooling production and component production, and monitoring of tooling wear, are tedious and time-consuming. Correction of errors, variations, and tooling repair continues to require welding and hand grinding.
Thus, while improvements have been made in the production of tooling having complex geometric shapes, problems remain which limit the ability of each of the prior art methods to accurately replicate the nuances of the master model in production tooling. In particular, data entry with a stylus is hampered by inaccuracies introduced at the edges of shapes. Accordingly, the need exists for tooling design and production methods which capture all of the features of engineered components, permit the correction of data errors present in CAD and NC data bases, and enable the entry of design improvements into CAD or NC data without requiring complete data re-entry. The need further exists to permit dimensional checks of master models, production tooling, and worn tooling against the CAD data or NC data bases, to eliminate the need for direct physical measurement.